The universe is no place for megastars

IT APPEARS there is a limit to how big stars can grow in today’s universe&colon; about 200 times the mass of our sun.

Astronomers used to think the size of the biggest stars in a cluster was related to the ratio, say, of the number of small sun-like stars to the number of bigger stars with 10 times the sun’s mass. Applying this ratio to R136a, which is the largest cluster of stars in our galaxy in which individual stars are discernible, the biggest star should have more than 600 times the mass of the sun. But its largest star is only about 150 solar masses and the largest known star in our galaxy is about 200 solar masses – making astronomers suspect that stars had a size limit.

Now Sally Oey of the University of Michigan at Ann Arbor and colleagues have strong support for a size limit in a

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